1. Field of the Invention
This invention relates to a freewheeling hub device for a bicycle, more particularly to a freewheeling hub device which can release the coupling between a sprocket wheel and a hub shell when a sudden termination of the rotation of the sprocket wheel occurs while a bicycle wheel continues moving due to the action of inertia.
2. Description of the Related Art
The freewheel of a bicycle is generally driven by a chain drive through a free-sprocket. In U.S. Pat. No. 5,718,315, a freewheeling hub device includes a hub shell which is connected to the freewheel spokes of a bicycle wheel and which has a through hole to receive a wheel axle, a driving barrel which is sleeved onto the axle and which has an externally threaded end inserted into the hub shell and an opposite end fastened to a sprocket wheel of the bicycle, a coupling socket which is mounted within the hub shell around the axle, and a connecting spring which is mounted within the hub shell around the coupling socket and which engages a sliding member that is slidable along the axle. The coupling socket has an internally threaded portion which is rotated to screw-in the externally threaded end when the driving barrel is rotated with the sprocket wheel, and has a friction wall which frictionally engages the hub shell upon a full threaded engagement of the internally threaded portion for forward movement of the bicycle wheel. When the sprocket wheel is rotated in the opposite direction, the driving barrel is synchronously rotated, thereby causing the screw-out movement of the coupling socket to disengage from the hub shell so as to result in idle running of the sprocket wheel.
As such, when the rotation of the sprocket wheel for forward movement of the bicycle wheel is terminated (i.e. the rider stops turning the pedals of the bicycle), and when the bicycle is pulled to move backward using the rider""s hands, since the coupling socket remains in engagement with the hub shell, the driving barrel, as well as the pedals, is also rotated with the hub shell, thereby resulting in a tendency to injury the rider""s legs.
The object of the present invention is to provide a freewheeling hub device in which the driving barrel is disengaged from the hub shell once the rotation of the driving barrel for forward movement of the bicycle is suddenly terminated while the bicycle wheel continues moving due to the action of inertia, thereby resulting in idle running of the hub shell without rotating the driving barrel as well as the pedals.
According to this invention, the freewheeling hub device includes a hub shell, a driving barrel, a coupling socket, a sliding member, a connecting spring, and a coiled spring which are adapted to be mounted rotatably on an axle of a bicycle. The hub shell has first and second lateral ends which are disposed opposite to each other in an axial direction parallel to the axle, and an inner peripheral wall which extends in the axial direction to communicate the first and second lateral ends and which defines a through hole. The inner peripheral wall has a first wall portion and a second wall portion respectively proximate to the first and second lateral ends, and an intermediate wall portion which is disposed between the first and second wall portions and which defines a shoulder. The driving barrel is rotatable relative to the hub shell, and includes a head portion which is disposed outwardly of the first lateral end and which is adapted to be rotated with a sprocket wheel of the bicycle, and an externally threaded portion which is disposed opposite to the head portion in the axial direction and which extends into the through hole so as to be located at the intermediate wall portion. The coupling socket is disposed rotatably and movably in the through hole in the axial direction, and includes a coupling end and an engaging end opposite to each other in the axial direction. The engaging end has a friction wall which confronts the intermediate wall portion, and an internally threaded portion which is disposed opposite to the friction wall in a direction radial to the axial direction to be movable in the axial direction between a fully engaged position, where the externally threaded portion is in a full threaded engagement with the internally threaded portion as a result of a clockwise rotation of the driving barrel relative to the coupling socket, which corresponds to a forward movement of the bicycle wheel, and the friction wall is frictionally engaged with the intermediate wall portion as a result of the full threaded engagement, and a partially engaged position, where the externally threaded portion is in a partial threaded engagement with the internally threaded portion as a result of a screwing-out movement of the internally threaded portion relative to the externally threaded portion, and the friction wall is disengaged from the intermediate wall portion. The sliding member is adapted to sleeve on the axle, and is movable in the axial direction. The connecting spring is mounted in the through hole, and interconnects the coupling socket and the sliding member. The coiled spring is mounted in the through hole, and includes a securing end which is connected to the coupling end of the coupling socket, and an abutting end which is disposed opposite to the securing end in the axial direction and which abuts against the shoulder. Thus, a sudden termination of the clockwise rotation of the driving barrel, while the bicycle wheel continues with the forward movement due to the action of inertia, imparts a force to the abutting end, which is subsequently transmitted along the coiled spring to the securing end so as to drive the coupling socket to rotate in the clockwise direction to permit the screwing-out movement of the internally threaded portion relative to the externally threaded portion, thereby placing the internally threaded portion in the partially engaged position.